The picket fence effect occurs when the signal analysed contains frequency components falling between integer multiples of the sample frequency. Their energy is spread over adjacent components. This leakage can be controlled by using application-specific windowing functions.
To illustrate the effect using FlexPro, one can generate a wobbled cosine signal (10,000 samples, frequency varying from 16 to 32). Apply a time-frequency spectral analysis (amplitude, rectangular window, segment length 128) and create a contour plot (using a color spectrum) from it. Zooming into the frequency (x) range from 0 to 50 reveals the “Picket Fences”. Playing around with window functions shows their influence on this discretization artifact.